Plasma processing apparatus

ABSTRACT

A plasma processing apparatus performs a stable and accurate matching operation with high reproducibility in a power modulation process of modulating of a high frequency power to be supplied into a processing vessel in a pulse shape. In the plasma processing apparatus, an impedance sensor  96 A provided in a matching device performs a dual sampling averaging process on a RF voltage measurement value and an electric current measurement value respectively obtained from a RF voltage detector  100 A of a voltage sensor system and a RF electric current detector  108 A of an electric current sensor system by sampling-average-value calculating circuits  104 A and  112 A and by moving-average-value calculating circuits  106 A and  114 A. Thus, an update speed of a load impedance measurement value outputted from the impedance sensor  96 A can be matched well with a driving control speed of a motor in a matching controller.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a U.S. national phase application under 35 U.S.C.§371 of PCT Application No. PCT/JP2012/007798 filed on Dec. 5, 2012,which claims the benefit of Japanese Patent Application No. 2011-274391filed on Dec. 15, 2011, and U.S. Provisional Application Ser. No.61/585,755 filed on Jan. 12, 2012, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

The embodiments described herein pertain generally to a technique ofperforming a plasma process on a processing target substrate, andparticularly, to a capacitively coupled plasma processing apparatus inwhich a high frequency power to be supplied into a processing vessel ismodulated in a pulse shape.

BACKGROUND

A capacitively coupled plasma processing apparatus includes an upperelectrode and a lower electrode arranged in parallel to each otherwithin a processing vessel. A processing target substrate (e.g., asemiconductor wafer, a glass substrate, etc) is mounted on the lowerelectrode, and a high frequency power having a frequency (typically,about 13.56 MHz or higher) suitable for plasma generation is applied tothe upper electrode or the lower electrode. Electrons are accelerated bya high frequency field generated between the two facing electrodes byapplying the high frequency power, and plasma is generated as a resultof ionization by collision between the electrons and a processing gas.Through a gas phase reaction or a surface reaction of radicals or ionsincluded in the plasma, a thin film is formed on the substrate, or amaterial or a thin film on a surface of the substrate is etched.

Recently, as a design rule is getting more miniaturized in amanufacturing process of a semiconductor device or the like, higherlevel of dimensional accuracy is required in, especially, plasmaetching. Further, it is required to increase etching selectivity againsta mask or an underlying film and to improve etching uniformity in theentire surface of a substrate. For this reason, pressure and ion energyin a processing region within a chamber tends to be reduced, and a highfrequency power having a high frequency equal to or higher than about 40MHz is used.

However, as the pressure and the ion energy are reduced, an influence ofa charging damage, which has been negligible conventionally, can be nomore neglected. That is, in a conventional plasma processing apparatushaving high ion energy, no serious problem may occur even when a plasmapotential is non-uniform in the entire surface of the substrate.However, if the ion energy is lowered at a lower pressure, thenon-uniformity of the plasma potential in the entire surface of thesubstrate may easily cause the charging damage on a gate oxide film.

In this regard, a method of modulating power of a high frequency powerused for plasma generation to an on/off (or H level/L level) pulsehaving a controllable duty ratio (hereinafter, referred to as “firstpower modulation process”) has been considered effective (PatentDocument 1). According to this power modulation process, a plasmageneration state in which plasma of a processing gas is being generatedand a plasma non-generation state in which plasma is not being generatedare alternately repeated at a preset cycle during a plasma etchingprocess. Accordingly, as compared to a typical plasma process in whichplasma is continuously generated from the beginning of the process tothe end thereof, a time period during which plasma is continuouslygenerated may be shortened. Accordingly, the amount of electric chargesintroduced into a processing target substrate from the plasma at onetime or the amount of electric charges accumulated on the surface of theprocessing target substrate may be reduced, so that the charging damageis suppressed from being generated. Therefore, a stable plasma processcan be performed and reliability of the plasma process can be improved.

Further, conventionally, in the capacitively coupled plasma processingapparatus, a RF bias method is widely employed. In this RF bias method,a high frequency power having a relatively low frequency (typically,about 13.56 MHz or lower) is applied to the lower electrode on which thesubstrate is mounted, and ions in the plasma are accelerated andattracted to the substrate by a negative bias voltage or a sheathvoltage generated on the lower electrode. In this way, by acceleratingthe ions in the plasma and bringing them into collision with the surfaceof the substrate, a surface reaction, anisotropic etching ormodification of a film may be facilitated.

However, when performing the etching process to form via holes orcontact holes by using the capacitively coupled plasma etchingapparatus, a so-called micro-loading effect may occur. That is, anetching rate may differ depending on the hole size, so that it isdifficult to control an etching depth. Especially, the etching ratetends to be higher at a large area such as a guide ring (GR), whereasthe etching rate tends to be lower at a small via in which CF-basedradicals are difficult to be introduced.

In this regard, a method of modulating power of a high frequency powerused for ion attraction to a first level/second level (or on/off) pulsehaving a controllable duty ratio (hereinafter, referred to as “secondpower modulation process”) has been considered effective. According tothe second power modulation process, a period of maintaining arelatively high power of the first level (H level) suitable for etchinga preset film on the processing target substrate and a period ofmaintaining a relatively low power of the second level (L level) as ahigh frequency power for ion attraction suitable for depositing polymeron a preset film on the processing target substrate are alternatelyrepeated at a certain cycle. Accordingly, at an area having a largerhole size, a proper polymer layer may be deposited on the preset film ata higher deposition rate, so that the etching may be suppressed. Thus,an undesirable micro-loading effect may be reduced, and it may bepossible to perform an etching process with a high selectivity and ahigh etching rate.

REFERENCES

Patent Document 1: Japanese Patent Laid-open Publication No. 2009-071292

Patent Document 2: Japanese Patent Laid-open Publication No. 2009-033080

Patent Document 3: Japanese Patent Laid-open Publication No. 2010-238881

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the first power modulation process or the second power modulationprocess as described above, a matching operation of a matching deviceprovided in a high frequency transmission line for transmitting a highfrequency power to plasma within a processing vessel from a highfrequency power supply is considered as a problem to be solved. That is,the matching device is operated such that load impedance including amatching circuit is matched with impedance on the side of a highfrequency power supply in order to most efficiently transmit the highfrequency power outputted from the high frequency power supply to theplasma within the processing vessel. However, if the high frequencypower is modulated in a pulse shape by the first power modulationprocess or the second power modulation process as described above,impedance of a plasma load is synchronized with a pulse and thusregularly changed, so that it becomes difficult to make the matchingoperation following this change.

In particular, it is cumbersome that a reflection wave reverselyreturning from the plasma back to the high frequency power supplythrough the high frequency transmission line includes not only afundamental frequency reflection wave corresponding to the highfrequency power but also a different frequency reflection wave such asdistortion of a harmonic wave or a modulated wave according to afrequency of the power modulation. An object is to carry out a matchingoperation at a high speed with accuracy to reduce a power of thefundamental frequency reflection wave as low as possible by respondingonly to the fundamental frequency reflection wave without being affectedby this different frequency reflection wave.

In this regard, conventionally, during a single cycle of powermodulation, a matching operation is stopped for a time period duringwhich a high frequency power on which the power modulation is performedis off (or at L level), and the matching operation is carried out for atime period during which the high frequency power is on (or at H level)(Patent Document 2). However, in each cycle of power modulation, aplasma status is greatly changed at the time of starting or right beforeending an on (or H level) period. If a matching operation is carried outfollowing the change in the plasma transient state, a reactance element(for example, a capacitor) within a matching device is operated slightlyand repeatedly. As a result, stabilization of plasma is securely madeand a plasma process becomes unstable, and also, a life of the reactanceelement is shortened. To solve this problem, in each cycle of powermodulation, during an on-period (or H level) as well as during anoff-period (or L level), the matching operation is controlled not to beperformed for a certain period of time (transient time) after theon-period is started (Patent Document 3).

However, in recent years, even if any one of the first and second powermodulation processes is used, in order to improve or increase atechnical effect based on the power modulation process and processperformance, or in order to increase a process margin, a plasmaprocessing apparatus is required to have a wider range (for example, 10%to 90%) of a duty ratio than a conventional range (25% to 80%) and alsorequired to have a higher range (for example, 100 Hz to 100 kHz) of apulse frequency of the power modulation than a conventional range (0.25Hz to 100 Hz). Therefore, for example, conditions including a duty ratioof 10% and a pulse frequency for power modulation of 90 kHz may beselected. According to the conventional method in which the matchingoperation of the matching device is intermittently stopped in each cycleof power modulation, if a pulse frequency for power modulation is on theorder of kHz or 10 kHz as such, it is not possible to follow a change inload (plasma) impedance, and malfunction or life-shortening ofcomponents of an operation system in the matching device may be caused.Therefore, it is difficult to be applicable for a power modulationprocess with a high pulse frequency.

Further, conventionally, with respect to a high frequency power on whichthe power modulation is not performed, any specific control has not beencarried out to a matching device provided on the high frequencytransmission line thereof. Therefore, the corresponding matching deviceis not synchronized with the power modulation performed on other highfrequency powers, but carries out a typical matching operation ofresponding to a change in load (plasma) impedance every moment(continuously) in the same manner as a case where only the highfrequency power on which the power modulation is not performed in thehigh frequency transmission line is applied to the plasma within theprocessing vessel. However, it has been difficult to stably andaccurately establish a fully matched state or a semi-matched statethrough such a typical matching operation. Further, if the frequency ofpower modulation is on the order of kHz or 10 kHz as described above, amatching problem in the high frequency power on which power modulationis not performed becomes very conspicuous.

In view of the foregoing, example embodiments provide a capacitivelycoupled plasma processing apparatus capable of performing a stable andaccurate matching operation with high reproducibility in the first orsecond power modulation process of modulating the high frequency powerto be supplied into the processing vessel in the pulse shape.

Means for Solving the Problems

In a first example embodiment, a plasma processing apparatus generatesplasma by high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performs a process on the substrate held on thefirst electrode under the plasma. The plasma processing apparatusincludes a first high frequency power supply configured to output afirst high frequency power; a first high frequency transmission lineconfigured to transmit the first high frequency power outputted from thefirst high frequency power supply to the first electrode; a firstmatching device configured to match impedance on the side of the firsthigh frequency power supply with load impedance on the first highfrequency transmission line; a second high frequency power supplyconfigured to output a second high frequency power; a second highfrequency transmission line configured to transmit the second highfrequency power outputted from the second high frequency power supply toany one of the first electrode and the second electrode; a secondmatching device configured to match impedance on the side of the secondhigh frequency power supply with load impedance on the second highfrequency transmission line; and a high frequency power modulation unitconfigured to control the second high frequency power supply such that afirst period during which the second high frequency power is on or has afirst level and a second period during which the second high frequencypower is off or has a second level lower than the first level isalternately repeated at a preset pulse frequency. Further, the firstmatching device includes a matching circuit having a variable reactanceelement, which is controllable, provided on the first high frequencytransmission line; a sampling-average-value calculating circuitconfigured to sample voltage detection signals and electric currentdetection signals corresponding to the first high frequency power on thefirst high frequency supply line with a preset sampling frequency andcalculate an average value of these signals during a first monitoringtime set for both of the first period and the second period in eachcycle of the pulse frequency; a moving-average-value calculating circuitconfigured to calculate a moving average value of the voltage detectionsignals and the electric current detection signals based on an averagevalue obtained from the sampling-average-value calculating circuit ineach cycle; a load impedance-measurement-value calculating circuitconfigured to calculate a measurement value of the load impedance withrespect to the first high frequency power supply based on the movingaverage value of the voltage detection signals and the electric currentdetection signals obtained from the moving-average-value calculatingcircuit; and a matching controller configured to vary a reactance of thevariable reactance element such that the measurement value of the loadimpedance obtained from the load impedance-measurement-value calculatingcircuit is equal or approximate to a preset matching point correspondingto impedance on the side of the first high frequency power supply.

In a second example embodiment, a plasma processing apparatus generatesplasma by high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performs a process on the substrate held on thefirst electrode under the plasma. The plasma processing apparatusincludes a first high frequency power supply configured to output afirst high frequency power; a first high frequency transmission lineconfigured to transmit the first high frequency power outputted from thefirst high frequency power supply to the first electrode; a firstmatching device configured to match impedance on the side of the firsthigh frequency power supply with load impedance on the first highfrequency transmission line; a second high frequency power supplyconfigured to output a second high frequency power; a second highfrequency transmission line configured to transmit the second highfrequency power outputted from the second high frequency power supply toany one of the first electrode and the second electrode; a secondmatching device configured to match impedance on the side of the secondhigh frequency power supply with load impedance on the second highfrequency transmission line; and a high frequency power modulation unitconfigured to control the second high frequency power supply such that afirst period during which the second high frequency power is on or has afirst level and a second period during which the second high frequencypower is off or has a second level lower than the first level isalternately repeated at a preset pulse frequency. Further, the firstmatching device includes a matching circuit having a variable reactanceelement, which is controllable, provided on the first high frequencytransmission line; a sampling-average-value calculating circuitconfigured to sample measurement values of the load impedance on thefirst high frequency transmission line with a preset sampling frequencyand calculate an average value of the measurement values during a firstmonitoring time set for both of the first period and the second periodin each cycle of the pulse frequency; a moving-average-value calculatingcircuit configured to calculate a moving average value of themeasurement values of the load impedance based on the average valueobtained from the sampling-average-value calculation circuit in eachcycle; and a matching controller configured to vary a reactance of thevariable reactance element such that the moving average value of themeasurement values of the load impedance obtained from themoving-average-value calculating circuit is equal or approximate to apreset matching point corresponding to the impedance on the side of thefirst high frequency power supply.

In a third example embodiment, a plasma processing apparatus generatesplasma by high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performs a process on the substrate held on thefirst electrode under the plasma. The plasma processing apparatusincludes a first high frequency power supply configured to output afirst high frequency power; a first high frequency transmission lineconfigured to transmit the first high frequency power outputted from thefirst high frequency power supply to any one of the first electrode andthe second electrode; a first matching device configured to matchimpedance on the side of the first high frequency power supply with loadimpedance on the first high frequency transmission line; a second highfrequency power supply configured to output a second high frequencypower; a second high frequency transmission line configured to transmitthe second high frequency power outputted from the second high frequencypower supply to the first electrode; a second matching device configuredto match impedance on the side of the second high frequency power supplywith load impedance on the second high frequency transmission line; anda high frequency power modulation unit configured to control the secondhigh frequency power supply such that a first period during which thesecond high frequency power is on or has a first level and a secondperiod during which the second high frequency power is off or has asecond level lower than the first level is alternately repeated at apreset pulse frequency. Further, the first matching device includes amatching circuit having a variable reactance element, which iscontrollable, provided on the first high frequency transmission line; asampling-average-value calculating circuit configured to samplemeasurement values of the load impedance on the first high frequencytransmission line with a preset sampling frequency and calculate anaverage value of the measurement values during a first monitoring timeset for both of the first period and the second period in each cycle ofthe pulse frequency; a moving-average-value calculating circuitconfigured to calculate a moving average value of the measurement valuesof the load impedance based on the average value obtained from thesampling-average-value calculation circuit in each cycle; and a matchingcontroller configured to vary a reactance of the variable reactanceelement such that the moving average value of the measurement values ofthe load impedance obtained from the moving-average-value calculatingcircuit is equal or approximate to a preset matching point correspondingto the impedance on the side of the first high frequency power supply.

In a fourth example embodiment, a plasma processing apparatus generatesplasma by high frequency electric discharge of a processing gas betweena first electrode and a second electrode which are provided to face eachother within an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performs a process on the substrate held on thefirst electrode under the plasma. The plasma processing apparatusincludes a first high frequency power supply configured to output afirst high frequency power; a first high frequency transmission lineconfigured to transmit the first high frequency power output from thefirst high frequency power supply to any one of the first electrode orthe second electrode; a first matching device configured to matchimpedance on the first high frequency power supply side with its loadside impedance in the first high frequency transmission line; a secondhigh frequency power supply configured to output a second high frequencypower; a second high frequency transmission line configured to transmitthe second high frequency power output from the second high frequencypower supply to the first electrode; a second matching device configuredto match impedance on the second high frequency power supply side withits load side impedance in the second high frequency transmission line;and a high frequency power modulation unit configured to control thesecond high frequency power supply such that a first period in whichpower of the second high frequency power is on or at a first level and asecond period in which power of the second high frequency power is offor at a second level lower than the first level repeat alternately in apreset pulse cycle. Further, the first matching device includes amatching circuit including a controllable reactance element, which iscontrollable, provided in the first high frequency transmission line; asampling-average-value calculating circuit configured to samplemeasurement values of the load side impedance obtained from the firsthigh frequency transmission line with a preset sampling frequency andcalculate an average value of the measurement values during a firstmonitoring time set for both of the first and second periods in a singlecycle of the pulse frequency; a moving-average-value calculating circuitconfigured to obtain a moving average value of the measurement values ofthe load side impedance based on an average value of each cycle obtainedfrom the sampling-average-value calculating circuit; and a matchingcontroller configured to control a reactance of the reactance elementsuch that the moving average value of the measurement values of the loadside impedance obtained from the moving-average-value calculatingcircuit is equal or close to a preset matching point corresponding tothe impedance on the first high frequency power supply side.

In a fifth example embodiment, plasma processing apparatus generatesplasma by high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performs a process on the substrate held on thefirst electrode under the plasma. The plasma processing apparatusincludes a high frequency power supply; a high frequency transmissionline configured to transmit the high frequency power outputted from thehigh frequency power supply to any one of the first electrode and thesecond electrode; a matching device configured to match impedance on theside of the high frequency power supply with load impedance on the highfrequency transmission line; and a high frequency power modulation unitconfigured to control the high frequency power supply such that a firstperiod during which the high frequency power is on and a second periodduring which the high frequency power is off is alternately repeated ata preset pulse frequency. Further, the matching device includes amatching circuit having a variable reactance element, which iscontrollable, provided on the high frequency transmission line; asampling-average-value calculating circuit configured to sample voltagedetection signals and electric current detection signals correspondingto the high frequency power on the high frequency supply line with apreset sampling frequency and calculate an average value of thesesignals during a monitoring time set for the first period in each cycleof the pulse frequency; a moving-average-value calculating circuitconfigured to calculate a moving average value of the voltage detectionsignals and the electric current detection signals based on the averagevalue obtained from the sampling-average-value calculating circuit ineach cycle; a load impedance-measurement-value calculating circuitconfigured to calculate a measurement value of the load impedance withrespect to the high frequency power supply based on the moving averagevalue of the voltage detection signals and the electric currentdetection signals obtained from the moving-average-value calculatingcircuit; and a matching controller configured to vary a reactance of thevariable reactance element such that the measurement value of the loadimpedance obtained from the load impedance-measurement-value calculatingcircuit is equal or approximate to a preset matching point correspondingto the impedance on the side of the high frequency power supply.

In a sixth example embodiment, a plasma processing apparatus generatesplasma by high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performs a process on the substrate held on thefirst electrode under the plasma. The plasma processing apparatusincludes a high frequency power supply; a high frequency transmissionline configured to transmit the high frequency power outputted from thehigh frequency power supply to any one of the first electrode and thesecond electrode; a matching device configured to match impedance on theside of the high frequency power supply with load impedance on the highfrequency transmission line; and a high frequency power modulation unitconfigured to control the high frequency power supply such that a firstperiod during which the high frequency power is on and a second periodduring which the high frequency power is off is alternately repeated ata preset pulse frequency. Further, the matching device includes amatching circuit having a variable reactance element, which iscontrollable, provided on the high frequency transmission line; asampling-average-value calculating circuit configured to sample voltagedetection signals and electric current detection signals correspondingto the high frequency power on the high frequency supply line with apreset sampling frequency and calculate an average value of thesesignals during a monitoring time set for the first period in each cycleof the pulse frequency; a moving-average-value calculating circuitconfigured to calculate a moving average value of the voltage detectionsignals and the electric current detection signals based on the averagevalue obtained from the sampling-average-value calculating circuit ineach cycle; a load impedance-measurement-value calculating circuitconfigured to calculate a measurement value of the load impedance withrespect to the high frequency power supply based on the moving averagevalue of the voltage detection signals and the electric currentdetection signals obtained from the moving-average-value calculatingcircuit; and a matching controller configured to vary a reactance of thevariable reactance element such that the measurement value of the loadimpedance obtained from the load impedance-measurement-value calculatingcircuit is equal or approximate to a preset matching point correspondingto the impedance on the side of the high frequency power supply.

Effect of the Invention

In accordance with the example embodiments, with the above-describedconfiguration and operation, a plasma processing apparatus can perform astable and accurate matching operation with high reproducibility in afirst modulation process or a second power modulation process ofmodulating of a high frequency power to be supplied into a processingvessel in a pulse shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a configuration of acapacitively coupled plasma processing apparatus in accordance with anexample embodiment.

FIG. 2A is a waveform diagram of a high frequency power showing anexample of a power modulation in the plasma processing apparatus.

FIG. 2B is a waveform diagram of a high frequency power showing anotherexample of the power modulation in the plasma processing apparatus.

FIG. 3A shows spectra of a high frequency power on which the powermodulation is performed and its side bands (modulation parts).

FIG. 3B shows spectra of a reflection wave in a case where a matchingoperation is performed.

FIG. 4A shows spectra of a high frequency power on which the powermodulation is not performed and its side bands (modulation parts).

FIG. 4B shows spectra of a reflection wave in a case where a matchingoperation is performed.

FIG. 5 is a block diagram showing a configuration of a matching deviceand a high frequency power supply for plasma generation.

FIG. 6 is a block diagram showing an internal configuration of thematching device of FIG. 5.

FIG. 7 is a block diagram showing a configuration of a matching deviceand a high frequency power supply for ion attraction.

FIG. 8 is a block diagram showing an internal configuration of thematching device of FIG. 7.

FIG. 9 provides waveform diagrams for explaining operations of thematching device in accordance with the example embodiment.

FIG. 10 provides diagrams for explaining an operation of a movingaverage value calculation in accordance with the example embodiment.

FIG. 11 provides diagrams for explaining an operation of a movingaverage value calculation in accordance with the example embodiment.

FIG. 12 shows a distribution (example) of matching operation points onthe Smith chart in accordance with the example embodiment.

FIG. 13 is a block diagram showing a configuration of an impedancesensor in accordance with a modification example.

FIG. 14 is a block diagram showing a configuration of an impedancesensor in accordance with a modification example.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, example embodiments will be explained with reference to theaccompanying drawings.

<Configuration of Plasma Processing Apparatus>

FIG. 1 shows a configuration of a plasma processing apparatus inaccordance with an example embodiment. This plasma processing apparatusis configured as a capacitively coupled (parallel plate type) plasmaetching apparatus in which dual high frequency powers are applied to alower electrode. By way of example, the plasma processing apparatusincludes a cylindrical decompression chamber (processing vessel) 10 madeof, but not limited to, aluminum having an alumite-treated (anodicallyoxidized) surface. The chamber 10 is grounded.

A circular columnar susceptor supporting member 14 is provided on aninsulating plate 12 such as ceramic on a bottom of the chamber 10, and asusceptor 16 made of, but not limited to, aluminum is provided on thesusceptor supporting member 14. The susceptor 16 serves as a lowerelectrode, and a processing target substrate, e.g., a semiconductorwafer W is mounted on the susceptor 16.

An electrostatic chuck 18 configured to hold the semiconductor wafer Wis provided on a top surface of the susceptor 16. The electrostaticchuck 18 includes a pair of insulating layers or insulating sheets; andan electrode 20 embedded therebetween. The electrode 20 is made of aconductive film and is electrically connected with a DC power supply 24via a switch 22. The semiconductor wafer W can be held on theelectrostatic chuck 18 by an electrostatic adsorptive force generated bya DC voltage applied from the DC power supply 24. In order to improveetching uniformity, a focus ring 26 made of, but not limited to, siliconis provided on the top surface of the susceptor 16 to surround theelectrostatic chuck 18. A cylindrical inner wall member 28 made of, butnot limited to, quartz is attached to side surfaces of the susceptor 16and the susceptor supporting member 14.

A coolant path 30 extended in, e.g., a circumferential direction isprovided within the susceptor supporting member 14. A coolant of apreset temperature, e.g., cooling water from an external chiller unit(not shown) is supplied into and circulated through the coolant path 30via pipelines 32 a and 32 b. A processing temperature of thesemiconductor wafer W on the susceptor 16 can be controlled by adjustingthe temperature of the coolant. Further, a heat transfer gas, e.g., a Hegas from a heat transfer gas supplying device (not shown) is suppliedinto a gap between a top surface of the electrostatic chuck 18 and arear surface of the semiconductor wafer W through a gas supply line 34.

The susceptor 16 is electrically connected with high frequency powersupplies 36 and 38 via matching unit devices 40 and 42, respectively,and a common power supply conductor (for example, a power supply rod)44. One high frequency power supply 36 outputs a high frequency powerRF1 having a frequency f_(RF1) (for example, 100 MHz) suitable forplasma generation. Meanwhile, the other high frequency power supply 38outputs a high frequency power RF2 having a frequency f_(RF2) (forexample, 13.56 MHz) suitable for ion attraction to the semiconductorwafer W on the susceptor 16 from the plasma.

As such, the matching device 40 and the power supply rod 44 constitute apart of a high frequency transmission line (high frequency transmissionpath) 43 configured to transmit the high frequency power RF1 for plasmageneration from the high frequency power supply 36 to the susceptor 16.Meanwhile, the matching device 42 and the power supply rod 44 constitutea part of a high frequency transmission line (high frequencytransmission path) 45 configured to transmit the high frequency powerRF2 for ion attraction from the high frequency power supply 38 to thesusceptor 16.

An upper electrode 46 having a ground potential is provided at a ceilingof the chamber 10, facing the susceptor 16 in parallel. The upperelectrode 46 includes an electrode plate 48 having a multiple number ofgas discharge holes 48 a and made of, e.g., a silicon-containingmaterial such as Si or SiC; and an electrode supporting body 50detachably supporting the electrode plate 48 and made of a conductivematerial such as aluminum having an alumite-treated surface. A plasmageneration space or a processing space PA is formed between the upperelectrode 46 and the susceptor 16.

The electrode supporting body 50 has a gas buffer room 52 formedtherein. The electrode supporting body 50 also has, in its bottomsurface, a multiple number of gas holes 50 a extended from the gasbuffer room 52, and the gas holes 50 a communicate with the gasdischarge holes 48 a of the electrode plate 48, respectively. The gasbuffer room 52 is connected to a processing gas supply source 56 via agas supply line 54. The processing gas supply source 56 is provided witha mass flow controller (MFC) 58 and an opening/closing valve 60. If acertain processing gas (etching gas) is introduced into the gas bufferroom 52 from the processing gas supply source 56, the processing gas isthen discharged in a shower shape from the gas discharge holes 48 a ofthe electrode plate 48 into the processing space PA toward thesemiconductor wafer W on the susceptor 16. In this configuration, theupper electrode 46 also serves as a shower head that supplies theprocessing gas into the processing space PA.

Further, a passageway (not shown) in which a coolant, e.g., coolingwater flows may be provided within the electrode supporting body 50. Theentire upper electrode 46, especially, the electrode plate 48 iscontrolled to a preset temperature through the coolant by an externalchiller unit. Further, in order to stabilize the temperature controlover the upper electrode 46, a heater (not shown) including a resistanceheating device may be provided within or on a top surface of theelectrode supporting body 50.

An annular space formed between a sidewall of the chamber 10, and thesusceptor 16 and the susceptor supporting member 14 serves as a gasexhaust space, and a gas exhaust opening 62 of the chamber 10 is formedin a bottom of this gas exhaust space. The gas exhaust opening 62 isconnected to a gas exhaust device 66 via a gas exhaust line 64. The gasexhaust device 66 includes a vacuum pump such as a turbo molecular pumpand is configured to depressurize the inside of the chamber 10,particularly, the processing space PA to a required vacuum level.Further, a gate valve 70 configured to open and close aloading/unloading opening 68 for the semiconductor wafer W is providedat the sidewall of the chamber 10.

A main controller 72 includes one or more microcomputers and isconfigured to control an overall operation (sequence) of the apparatusand individual operations of respective components within the apparatus,particularly, the high frequency power supplies 36 and 38, the matchingdevices 40 and 42, the MFC 58, the opening/closing valve 60, the gasexhaust device 66, etc., according to software (program) and recipesstored in an external memory or an internal memory.

Further, the main controller 72 is connected to a man-machine interfacemanipulation panel (not shown) including an input device such as akeyboard and a display device such as a liquid crystal display and,also, connected to an external storage device (not shown) that storesvarious types of data such as various programs or recipes, settingvalues, etc. In the present example embodiment, the main controller 72is configured as a single control unit. However, it may be also possibleto adopt a configuration in which multiple control units divide up thefunctions of the main controller 72 individually or hierarchically.

A basic operation of single-sheet typed dry etching in the capacitivelycoupled plasma etching apparatus configured as described above isperformed as follows. First, the gate valve 70 is opened, and asemiconductor wafer W to be processed is loaded into the chamber 10 andmounted on the electrostatic chuck 18. Then, a processing gas, i.e., anetching gas (generally, a gaseous mixture) is introduced into thechamber 10 from the processing gas supply source 56 at a preset flowrate and a preset flow rate ratio, and the inside of the chamber 10 isevacuated to be a set vacuum pressure by the gas exhaust device 66.Further, the high frequency power RF1 (100 MHz) for plasma generationand the high frequency power RF2 (13.56 MHz) for ion attraction from thehigh frequency power supplies 36 and 38 are overlapped at preset powers,respectively, to be applied to the susceptor 16. Further, a DC voltagefrom the DC power supply 24 is applied to the electrode 20 of theelectrostatic chuck 18, so that the semiconductor wafer W is held on theelectrostatic chuck 18. The etching gas discharged from the upperelectrode 46 serving as the shower head is discharged under a highfrequency electric field between the two electrodes 46 and 16, so thatplasma is generated in the processing space PA. An etching target filmon a main surface of the semiconductor wafer W is etched by radicals orions included in the plasma.

In this capacitively coupled plasma etching apparatus, for example, tosolve the above-described charging damage, a first power modulationprocess of modulating the high frequency power RF1 for plasma generationoutputted from the high frequency power supply 36 in an on/off (or Hlevel/L level) pulse shape having a pulse frequency of, for example, 1kHz to 100 kHz with a duty ratio within a range of, for example, 10% to90% can be used for the etching process. Further, to solve theabove-described micro-loading effect, a second power modulation processof modulating the high frequency power RF2 for ion attraction outputtedfrom the high frequency power supply 38 in an on/off (or H level/Llevel) pulse shape having a pulse frequency of, for example, 100 Hz to50 kHz with a duty ratio within a range of, for example, 10% to 90% canalso be used for the etching process.

By way of example, if a dry etching process is carried out by the firstpower modulation process, a modulation control pulse signal PS thatdefines a pulse frequency f_(s) and a duty ratio D_(s) set for the powermodulation is sent from the main control unit 72 to the high frequencypower supply 36. The high frequency power supply 36 turns on/off thehigh frequency power RF1 for plasma generation in synchronization withthe modulation control pulse signal PS. Herein, assuming that a cycle,the on-period (first period) and the off-period (second period) of themodulation control pulse signal PS are set to T_(C), T_(on), andT_(off), respectively, relational expressions T_(C)=1/f_(S),T_(C)=T_(on)+T_(off), and D_(S)=T_(on)/(T_(on)+T_(off)) are established.

Meanwhile, in the first power modulation process, the high frequencypower supply 38 does not turn on/off the high frequency power RF2 forion attraction, but continuously outputs the high frequency power RF2for ion attraction. In this case, due to on/off of the high frequencypower RF1, impedance of plasma within the chamber 10 is changed betweentwo values. Therefore, a matching operation or a matching degree on thehigh frequency transmission line 45 is also changed between two statesin synchronization with on/off of the high frequency power RF1. To bemore specific, as described below, between the on-period T_(on) and theoff-period T_(off) constituting one cycle of the pulse frequency f_(s),a matching degree is different depending on a duration thereof, and iscloser to a fully matched state during a relatively long on-period ascompared with a short on-period. Also, there is made a difference in apower of the high frequency power RF2 on the high frequency transmissionline 45 accordingly.

That is, as depicted in FIG. 2A, if the on-period T_(on) is sufficientlylonger than the off-period T_(off) (if the duty ratio D_(s) issufficiently high), the matching degree is closer to a fully matchedstate during the on-period T_(on) than the off-period T_(off), and,thus, the power of the high frequency power RF2 is higher during theon-period T_(on) than the off-period T_(off).

On the contrary, as depicted in FIG. 2B, if the off-period T_(off) issufficiently longer than the on-period T_(on) (if the duty ratio D_(s)is sufficiently low), the matching degree is closer to a fully matchedstate during the off-period T_(off) than the on-period T_(on), and,thus, the power of the high frequency power RF2 is higher during theoff-period T_(off) than the on-period T_(on).

If the power modulation is performed on the high frequency power RF1 forplasma generation by the first power modulation process as such, in aprogressive wave heading toward the susceptor 16 within the chamber 10from the high frequency power supply 36 on the high frequencytransmission line 43, as depicted in FIG. 3A, there are includedfrequency components in side bands (modulation parts of the pulsefrequency) caused by the pulse frequency f_(s) around (at both sides of)the high frequency power RF1 on a frequency axis as well as the highfrequency power RF1. In this case, when a matching operation of thematching device 40 is carried out well and the matching is done well,the high frequency power RF1 is most efficiently absorbed into theplasma. Therefore, in a reflection wave that propagates on the highfrequency transmission line 43 in a backward direction from the plasmawithin the chamber 10, as depicted in FIG. 3B, a power of a fundamentalfrequency reflection wave having the same frequency f_(RF1) as the highfrequency power RF1 is remarkably decreased.

Meanwhile, in a power supply system on the side of the high frequencypower RF2 on which the power modulation is not performed, the highfrequency power RF2 is (changed) between two values in synchronizationwith on/off of the high frequency power RF1 as described above, and,thus, as depicted in FIG. 4A, there are included frequency components inside bands (modulation parts of the pulse frequency) caused by the pulsefrequency f_(s) as well as the high frequency power RF2, and thefundamental frequency reflection wave in the progressive wave and thereflection wave. Therefore, when a matching operation of the matchingdevice 42 is carried out well and the matching is done well, the highfrequency power RF2 is most efficiently absorbed into the plasma. Inthis case, in a reflection wave that propagates on the high frequencytransmission line 45 in a backward direction from the plasma within thechamber 10, as depicted in FIG. 4B, a power of a fundamental frequencyreflection wave having the same frequency f_(RF2) as the high frequencypower RF2 is remarkably decreased.

Further, even if the power modulation is performed on the high frequencypower RF2 for ion attraction by the second power modulation process,there are generated side bands accompanied with the same powermodulation as described above just by replacing the high frequency powerRF1 with the high frequency power RF2, and the same required capabilityas described above is provided to the matching operations of thematching devices 40 and 42.

<Configuration of High Frequency Power Supply and Matching Device>

FIG. 5 illustrates a configuration of the high frequency power supply 36for plasma generation and a matching device 40.

The high frequency power supply 36 includes an oscillator 80A configuredto generate a sine wave of a frequency (for example, 100 MHz) suitablefor plasma generation; a power amplifier 82A configured to control apower of the sine wave outputted from the oscillator 80A and amplify thepower with a variable gain or amplification factor; and a power supplycontrol unit 84A configured to directly control the oscillator 80A andthe power amplifier 82A in response to a control signal from the maincontrol unit 72. The main control unit 72 also outputs control signalsof typical power supply on/off or power interlock relation and data suchas power set values as well as the modulation control pulse signal PS tothe power supply control unit 84A. The main control unit 72 and thepower supply control unit 84A constitute a power modulation unit of ahigh frequency power RF1.

The high frequency power supply 36 also includes a RF power monitor 86Aprovided. The RF power monitor 86A includes a directional coupler, aprogressive wave power monitoring unit, and a reflection wave powermonitoring unit (which are not illustrated). Herein, the directionalcoupler extracts signals corresponding to a RF power (progressive wave)propagating on the high frequency transmission line 43 in a forwarddirection and a RF power (reflection wave) propagating on the highfrequency transmission line 43 in a backward direction. The progressivewave power monitoring unit is configured to output a signal indicating apower of a fundamental frequency progressive wave (about 100 MHz)included in the progressive wave propagating on the high frequencytransmission line 43 based on a progressive wave power detection signalextracted by the directional coupler. This signal, i.e., a fundamentalfrequency progressive wave power measurement value, is sent to the powersupply control unit 84A within the high frequency power supply 36 forpower feedback control and also sent to the main control unit 72 formonitor display. The reflection wave power monitoring unit is configuredto measure a power of a fundamental frequency reflection wave (about 100MHz) included in the reflection wave returning back to the highfrequency power supply 36 from plasma within the chamber 10, and also tomeasure a total power of all reflection wave spectra included in thereflection wave returning back to the high frequency power supply 36from plasma within the chamber 10. A fundamental frequency reflectionwave power measurement value outputted by the reflection wave powermonitoring unit is sent to the main control unit 72 for monitor display,and a total reflection wave power measurement value is sent to the powersupply control unit 84A within the high frequency power supply 36 as amonitor value for protecting the power amplifier.

The matching device 40 includes a matching circuit 88A includingmultiple, for example, two variable reactance elements (for example,capacitors or inductors) X_(H1) and X_(H2); a matching controller 94Aconfigured to vary a reactance of the reactance elements X_(H1) andX_(H2) via actuators, for example, motors (M) 90A and 92A; and animpedance sensor 96A configured to measure load impedance includingimpedance of the matching circuit 88A on the high frequency transmissionline 43.

The matching controller 94A is operated under control of the maincontrol unit 72 and configured to vary a reactance of the reactanceelements X_(H1) and X_(H2) by controlling the motors 90A and 92A byusing a measurement value of the load impedance measured by theimpedance sensor 96A as a feedback signal such that the measurementvalue of the load impedance can be equal or approximate to the matchingpoint (typically, about 50Ω) corresponding to impedance on the side ofthe high frequency power supply 36.

FIG. 6 illustrates an internal configuration of the impedance sensor96A. This impedance sensor 96A includes a RF voltage detector 100A of avoltage sensor system; a voltage-detection-signal generating circuit102A; a sampling-average-value calculating circuit 104A and amoving-average-value calculating circuit 106A; a RF electric currentdetector 108A of an electric current sensor system; an electriccurrent-detection-signal generating circuit 110A; asampling-average-value calculating circuit 112A and amoving-average-value calculating circuit 114A; and a load impedancecalculating circuit 116A.

The RF voltage detector 100A of the voltage sensor system is configuredto detect a voltage of the high frequency power on the high frequencytransmission line 43. The voltage-detection-signal generating circuit102A includes, for example, a superheterodyne filter circuit, and isconfigured to generate a voltage detection signal corresponding to thehigh frequency power RF1 through analogue filtering of a high frequencyvoltage detection signal obtained from the RF voltage detector 100A.

The sampling-average-value calculating circuit 104A is operated insynchronization with the power modulation and configured to samplevoltage detection signals obtained from the voltage-detection-signalgenerating circuit 102A with a preset frequency and calculate an averagevalue of these signals during a preset monitoring time T_(H) in eachcycle of the pulse frequency f_(s). In this configuration example,analogue voltage detection signals from the voltage-detection-signalgenerating circuit 102A are converted into digital signals by thesampling-average-value calculating circuit 104A. A clock ACK₁ forsampling and a RF1 monitor signal AS for indicating the monitoring timeT_(H) of the high frequency power RF1 are sent to thesampling-average-value calculating circuit 104A from the main controlunit 72. The sampling-average-value calculating circuit 104A is requiredto process large quantities of signals at a high speed insynchronization with the sampling clock ACK₁ of several tens of MHz ormore, and, thus, a FPGA (field programmable gate array) can be usedappropriately.

The moving-average-value calculating circuit 106A is configured tocalculate a moving average value of the voltage detection signals basedon an average value of each cycle obtained from thesampling-average-value calculating circuit 104A. That is, themoving-average-value calculating circuit 106A is configured to sampleconsecutive N average values of the voltage detection signals obtainedfrom the sampling-average-value calculating circuit 104A by a certaincycle, configured to calculate a moving average value with respect tothe N average values, and configured to move a sampling range on a timeaxis by a desired movement pitch to repeat the moving average valuecalculation. A value of the movement pitch can be set optionally. Themain control unit 72 outputs a clock ACK₂ for sampling to themoving-average-value calculating circuit 106A. The moving-average-valuecalculating circuit 106A is not particularly required to process signalsat a high speed, and, thus, a typical CPU can be used appropriatelytherefor.

The RF electric current detector 108A of the electric current sensorsystem is configured to detect an electric current of the high frequencypower on the high frequency transmission line 43. The electriccurrent-detection-signal generating circuit 110A has the sameconfiguration and the same function as the above-describedvoltage-detection-signal generating circuit 102A, and is configured togenerate electric current detection signals corresponding to the highfrequency power RF1. The sampling-average-value calculating circuit 112Ahas the same configuration and the same function as the above-describedsampling-average-value calculating circuit 104A, and is configured tosample electric current detection signals obtained from the electriccurrent-detection-signal generating circuit 110A with a preset frequencyand calculate an average value of these signals during a presetmonitoring time T_(H) in each cycle of the pulse frequency f_(s). Themoving-average-value calculating circuit 114A has the same configurationand the same function as the above-described moving-average-valuecalculating circuit 106A, and is configured to calculate a movingaverage value of electric current detection signals based on an averagevalue of each cycle obtained from the sampling-average-value calculatingcircuit 112A.

The load impedance calculating circuit 116A is configured to calculate ameasurement value of load impedance with respect to the high frequencypower supply 36 based on the moving average value of the voltagedetection signals from the moving-average-value calculating circuit 106Aand the moving average value of the electric current detection signalsobtained from the moving-average-value calculating circuit 114A. Themeasurement value of the load impedance outputted from the loadimpedance calculating circuit 116A is updated in synchronization withthe sampling clock ACK₂. The main control unit 72 outputs a clock ACK₃to the load impedance calculating circuit 116A. Typically, a measurementvalue of the load impedance outputted from the load impedancecalculating circuit 116A includes an absolute value and a phasemeasurement value of the load impedance.

The matching controller 94A within the matching device 40 is configuredto respond to the load impedance measurement value measured from theimpedance sensor 96A and vary a reactance of the reactance elementsX_(H1) and X_(H2) within the matching circuit 88A by controlling themotors 90A and 92A such that a phase of the load impedance measurementvalue is about zero (0) and an absolute value thereof is about 50Ω.

The load impedance measurement value outputted from the impedance sensor96A to the matching controller 94A is updated in synchronization withthe power modulation (precisely, on a cycle for moving average valuecalculation). The matching controller 94A does not stop a matchingoperation, i.e., does not stop the control of a reactance of thereactance elements X_(H1) and X_(H2) during the update, and continuouslycontrols the motors 90A and 92A such that the load impedance measurementvalue right before the update can be equal and approximate to thematching point.

In this example embodiment, a dual sampling averaging process isperformed on the RF voltage and electric current measurement values bythe sampling-average-value calculating circuits 104A and 112A and themoving-average-value calculating circuits 106A and 114A. As a result, anupdate speed of the load impedance measurement value outputted from theimpedance sensor 96A can be matched well with a driving control speed ofthe motors 90A and 92A (i.e., reactance control of the reactanceelements X_(H1) and X_(H2)) in the matching controller 94A. Thus, evenif a pulse frequency for power modulation is set on the order of severaltens of kHz or more, in a matching operation of the matching device 40,malfunction or life-shortening of operating components (particularly,reactance elements X_(H1) and X_(H2)) is not caused, and it is possibleto accurately follow a change in the load (plasma) impedance.

Further, in this example embodiment, as described above, automaticmatching is carried out such that a measurement value of the loadimpedance obtained based on the voltage detection signals and theelectric current detection signals corresponding to the high frequencypower RF1 obtained on the high frequency transmission line 43 can beequal or approximate to the matching point, and, thus, even if there arefrequency components in side bands (modulation parts of the pulsefrequency f_(s)) caused by the modulation frequency around (in bothsides of) the high frequency power RF1 on a frequency axis, a matchingoperation of the matching device 40 can have an effect on the highfrequency power RF1. Therefore, as depicted in FIG. 3B, a reflectionwave power monitor unit within the RF power monitor 86A can obtain amonitoring result that the power of the fundamental frequency reflectionwave f_(RF1) is remarkably decreased.

FIG. 7 illustrates a configuration of the high frequency power supply 38for ion attraction and the matching device 42 in accordance with thepresent example embodiment.

The high frequency power supply 38 includes an oscillator 80B configuredto generate a sine wave of a frequency (for example, 13.56 MHz) for ionattraction; a power amplifier 82B configured to control a power of thesine wave outputted from the oscillator 80B and amplify the power with avariable gain or amplification factor; a power supply control unit 84Bconfigured to directly control the oscillator 80B and the poweramplifier 82B in response to a control signal from the main control unit72; and a RF power monitor 86B. The components 80B to 86B within thehigh frequency power supply 38 respectively have the same configurationsand the same functions as the components 80A to 86A within the highfrequency power supply 36 except that the frequency (13.56 MHz) of theoscillator 80B is different from the frequency (100 MHz) of theoscillator 80A. Further, the main control unit 72 and the power supplycontrol unit 84B constitute a power modulation unit of a high frequencypower RF2.

The matching device 42 includes a matching circuit 88B includingmultiple, for example, two variable reactance elements (for example,capacitors or inductors) X_(L1) and X_(L2); a matching controller 94Bconfigured to vary a reactance of the reactance elements X_(L1) andX_(L2) via actuators, for example, motors (M) 90B and 92B; and animpedance sensor 96B configured to measure load impedance includingimpedance of the matching circuit 88B on the high frequency transmissionline 45.

The matching controller 94B is operated under control of the maincontrol unit 72 and configured to vary a reactance of the reactanceelements X_(L1) and X_(L2) by controlling the motors 90B and 92B byusing a measurement value of the load impedance measured by theimpedance sensor 96B as a feedback signal such that the measurementvalue of the load impedance can be equal or approximate to the matchingpoint (typically, about 50Ω) corresponding to impedance on the side ofthe high frequency power supply 38.

FIG. 8 illustrates an internal configuration of the impedance sensor96B. This impedance sensor 96B includes a RF voltage detector 100B of avoltage sensor system; a voltage-detection-signal generating circuit102B; a sampling-average-value calculating circuit 104B and amoving-average-value calculating circuit 106B; a RF electric currentdetector 108B of an electric current sensor system; an electriccurrent-detection-signal generating circuit 110B; asampling-average-value calculating circuit 112B and amoving-average-value calculating circuit 114B; and a load impedancecalculating circuit 116B.

The RF voltage detector 100B of the voltage sensor system is configuredto detect a voltage of the high frequency power on the high frequencytransmission line 45. The voltage-detection-signal generating circuit102B includes, for example, a superheterodyne filter circuit, and isconfigured to generate a voltage detection signal corresponding to thehigh frequency power RF1 through analogue filtering of a high frequencyvoltage detection signal obtained from the RF voltage detector 100B.

The sampling-average-value calculating circuit 104B is operated insynchronization with the power modulation and configured to sampleelectric current detection signals obtained from the electriccurrent-detection-signal generating circuit 110B with a preset frequencyand calculate an average value of these signals during a presetmonitoring time T_(L) in each cycle of the pulse frequency f_(s). Inthis configuration example, analogue electric current detection signalsfrom the electric current-detection-signal generating circuit 110B areconverted into digital signals by the sampling-average-value calculatingcircuit 104B. A clock BCK₁ for sampling and a RF2 monitor signal BS forindicating the monitoring time T_(L) of the high frequency power RF2 aresent to the sampling-average-value calculating circuit 104B from themain control unit 72.

The moving-average-value calculating circuit 106B is configured tocalculate a moving average value of the electric current detectionsignals based on an average value of each cycle obtained from thesampling-average-value calculating circuit 104B. That is, themoving-average-value calculating circuit 106B is configured to sampleconsecutive N average values of the electric current detection signalsobtained from the sampling-average-value calculating circuit 104B by acertain cycle, configure to calculate a moving average value withrespect to the N average values, and configured to move a sampling rangeon a time axis by a desired movement pitch to repeat the moving averagevalue calculation. A value of the movement pitch can be set optionally.

The RF electric current detector 108B of the electric current sensorsystem is configured to detect an electric current of the high frequencypower in the high transmission line 45. The electriccurrent-detection-signal generating circuit 110B has the sameconfiguration and the same function as the above-describedvoltage-detection-signal generating circuit 102B, and is configured togenerate electric current detection signals corresponding to the highfrequency power RF2. The sampling-average-value calculating circuit 112Bhas the same configuration and the same function as the above-describedsampling-average-value calculating circuit 104B, and is configured tosample electric current detection signals obtained from the electriccurrent-detection-signal generating circuit 110B with a preset frequencyand calculate an average value of these signals during a presetmonitoring time T_(RF2) in each cycle of the pulse frequency f_(s). Themoving-average-value calculating circuit 114B has the same configurationand the same function as the above-described moving-average-valuecalculating circuit 106B, and is configured to calculate a movingaverage value of electric current detection signals based on an averagevalue of each cycle obtained from the sampling-average-value calculatingcircuit 112B.

The load impedance calculating circuit 116B is configured to calculate ameasurement value of a load impedance with respect to the high frequencypower supply 38 based on the moving average value of the voltagedetection signals from the moving-average-value calculating circuit 106Band the moving average value of the electric current detection signalsobtained from the moving-average-value calculating circuit 114B. Themeasurement value of the load impedance outputted from the loadimpedance calculating circuit 116B is updated in synchronization with asampling clock BCK₂ for moving average value calculation. The maincontrol unit 72 outputs a required clock BCK₃ to the load impedancecalculating circuit 116B. Typically, a measurement value of the loadimpedance outputted from the load impedance calculating circuit 116Bincludes an absolute value and a phase measurement value of the loadside impedance.

The matching controller 94B within the matching device 42 is configuredto respond to the load impedance measurement value measured from theimpedance sensor 96B and vary a reactance of the reactance elementsX_(L1) and X_(L2) within the matching circuit 88B by controlling themotors 90B and 92B such that a phase of the load impedance measurementvalue is about zero (0) and an absolute value thereof is about 50Ω.

The load impedance measurement value outputted from the impedance sensor96B to the matching controller 94B is updated in synchronization withthe power modulation (precisely, on a cycle for moving average valuecalculation). The matching controller 94B does not stop a matchingoperation, i.e., does not stop the control of a reactance of thereactance elements X_(L1) and X_(L2) during the update, and continuouslycontrols the motors 90B and 92B such that the load impedance measurementvalue right before the update can be equal and approximate to thematching point.

In this example embodiment, a dual sampling averaging process isperformed on the RF voltage and electric current measurement values bythe sampling-average-value calculating circuits 104B and 112B and themoving-average-value calculating circuits 106B and 114B. As a result, anupdate speed of the load impedance measurement value outputted from theimpedance sensor 96B can be matched well with a driving control speed ofthe motors 90B and 92B (i.e., reactance control of the reactanceelements X_(L1) and X_(L2)) in the matching controller 94B. Thus, evenif a pulse frequency for power modulation is set on the order of severaltens of kHz or more, in a matching operation of the matching device 42,malfunction or life-shortening of operating components (particularly,reactance elements X_(L1) and X_(L2)) is not caused, and it is possibleto accurately follow a change in the load (plasma) impedance.

Further, in this example embodiment, as described above, automaticmatching is carried out such that a measurement value of the loadimpedance obtained based on the voltage detection signals and theelectric current detection signals corresponding to the high frequencypower RF2 obtained on the high frequency transmission line 45 can beequal or approximate to the matching point. That is, even if there arefrequency components in side bands (modulation parts of the pulsefrequency) caused by the modulation frequency f_(s) around (in bothsides of) the high frequency power RF2 on a frequency axis, a matchingoperation of the matching device 42 can have an effect on the highfrequency power RF2. Therefore, as depicted in FIG. 4B, a reflectionwave power monitor unit within the RF power monitor 86B can obtain amonitoring result that the power of the fundamental frequency reflectionwave f_(RF2) is remarkably decreased.

<Operation of Matching Device>

Hereinafter, referring to FIG. 9, as an example, operations of thematching devices 40 and 42 in the first power modulation process will beexplained in more detail.

When a dry etching process is performed by the first power modulationprocess, the main control unit 72 outputs a modulation control pulsesignal PS to the high frequency power supply 36 for plasma generation.The high frequency power supply 36 turns on/off the high frequency powerRF1 in synchronization with the modulation control pulse signal PS, asdepicted in FIG. 9.

In this case, a monitoring time T_(H) for a sampling averaging processsent to the sampling-average-value calculating circuits 104A and 112Awithin the matching device 40 of the high frequency power RF1 by amonitor signal AS from the main control unit 72 is set within anon-period T_(on) in each cycle of the pulse frequency f_(s). Desirably,as depicted in FIG. 9, the monitoring time T_(H) is set within timeranges except transient times T_(A1) and T_(A2) right after starting andright before ending the on-period T_(on) during which a power of theRF1-based reflection wave is abruptly increased on the high frequencytransmission line 43. Here, the monitoring time T_(H) is set only withinthe on-period T_(on), not within the off-period T_(off). Thus, thematching device 40 functions only when the high frequency power RF1 isturned on.

The sampling-average-value calculating circuits 104A and 112A samplevoltage detection signals and electric current detection signals insynchronization with a sampling clock ACK₁ during this monitoring timeT_(H) and then calculate average values thereof.

By way of example, a pulse frequency f_(s) is 10 kHz, a duty ratio D_(s)is 80%, a frequency of the sampling clock ACK₁ is 40 MHz, and themonitoring time T_(H) is half (50%) the length of the on-period T_(on).In this case, in each cycle of the pulse frequency f_(s), the samplingis carried out 1600 times during the monitoring time T_(H) in theon-period T_(on), to obtain one average value data a, which indicatesthe average of 1600 values.

As depicted in FIG. 10, the moving-average-value calculating circuit106A of the voltage sensor system within the matching device 40 receivesthe average data a outputted from the sampling-average-value calculatingcircuit 104A in each cycle of the pulse frequency f_(s); samplesconsecutive N average values a of the voltage detection signals at acycle T_(A) of a sampling clock ACK₂; calculates a moving average valueof the sampled N average value data a; and moves a sampling range on atime axis by a movement pitch according to the cycle T_(A) of thesampling clock ACK₂ to repeat the moving average value calculation.

By way of example, when the pulse frequency f_(s) is 10 kHz, if thecycle T_(A) of the sampling clock ACK₂ is 200 μsec (5 kHz in terms offrequency), as depicted in FIG. 10, a movement pitch (the number of dataupdated among average value data a at a front side on a time axis andaverage value data a at a rearmost side thereof through one-time movingaverage value calculation) is “2”. As such, if a value of the movementpitch is optionally set to “m” (m is an integer of 2 or more), afrequency of the sampling clock signal ACK₂ may be determined as being1/m times of the pulse frequency f_(s).

The moving-average-value calculating circuit 114A of the electriccurrent sensor system within the matching device 40 is also operated atthe substantially same time as the moving-average-value calculatingcircuit 106A of the voltage sensor system, and performs the same signalprocess on the average value of the electric current detection signals.

If the first power modulation process is used, in the matching device 40of the high frequency power RF1 for plasma generation, thesampling-average-value calculating circuits 104A and 112A perform signalprocesses on the sampling averages at a high speed during the monitoringtime T_(H) set within the on-period T_(on) (desirably, within time ragesexpect the transient time in which the power of the reflection wave ishigh) in each cycle of the pulse frequency f_(s), and themoving-average-value calculating circuits 106A and 114A perform signalprocesses on the moving averages for multiple cycles. Further, accordingto a load impedance measurement value, which is obtained from the loadimpedance calculating circuit 116A and updated in synchronization with asampling clock of the moving average, the matching controller 94Acontinuously controls a reactance of the reactance elements X_(H1) andX_(H2). Thus, even if the pulse frequency for the power modulation isset on the order of several tens of kHz or more and a duty ratio D_(s)is set to a certain level, in a matching operation of the matchingdevice 40, malfunction or life-shortening of operating components(particularly, reactance elements X_(H1) and X_(H2)) may not be caused,and it is possible to accurately follow the change in the load (plasma)impedance.

Meanwhile, in the first power modulation process, the modulation controlpulse signal PS is not sent to the high frequency power supply 38 forion attraction. Therefore, the high frequency power supply 38continuously outputs the high frequency power RF2 at a preset level.

In this case, a monitoring time T_(L) for a sampling averaging processsent to the sampling-average-value calculating circuits 104B and 112Bwithin the matching device 42 of the high frequency power RF2 by amonitor signal BS from the main control unit 72 is set for both of anon-period T_(on) and an off-period T_(off) in each cycle of the pulsefrequency f_(s). Desirably, as depicted in FIG. 9, the monitoring timeT_(L1) is set within time ranges except transient times T_(B1) andT_(B2) right after starting and right before ending the on-period T_(on)during which a power of the RF2-based reflection wave is abruptlyincreased on the high frequency transmission line 45. Meanwhile, anothermonitoring time T_(L2) is set within all time ranges of the off-periodT_(off).

The sampling-average-value calculating circuits 104B and 112B samplevoltage detection signals and electric current detection signals insynchronization with a sampling clock BCK₁ during the former monitoringtime T_(L1) in each cycle of the pulse frequency f_(s) and calculateaverage values b thereof. Then, the sampling-average-value calculatingcircuits 104B and 112B also sample voltage detection signals andelectric current detection signals in synchronization with the samplingclock BCK₁ during the latter monitoring time T_(L2) and calculateaverage values c thereof.

By way of example, a pulse frequency f_(s) is 10 kHz, a duty ratio D_(s)is 80%, a frequency of the sampling clock BCK₁ is 40 MHz, and the formermonitoring time T_(L1) is half (50%) the length of the on-period T_(on)and the latter monitoring time T_(L2) has the entire length of theoff-period T_(off). In this case, in each cycle of the pulse frequencyf_(s), the sampling is carried out 1600 times during the formermonitoring time T_(L1) to obtain one average value data b, whichindicates the average of 1600 values. Further, the sampling is carriedout 800 times during the latter monitoring time T_(L2) to obtain oneaverage value data c, which indicates the average of 800 values.

As depicted in FIG. 11, the moving-average-value calculating circuit106B of the voltage sensor system within the matching device 42 receivesthe average data b and c outputted from the sampling-average-valuecalculating circuit 104B in each cycle of the pulse frequency f_(s);samples consecutive N groups of the average values b and c of thevoltage detection signals at a cycle T_(B) of a sampling clock BCK₂;calculates a moving average of the N groups of the average value data band c; and moves a sampling range on a time axis by a movement pitchaccording to the cycle T_(B) of the sampling clock BCK₂ to repeat themoving average value calculation.

By way of example, when the pulse frequency f_(s) is 10 kHz, if thecycle T_(B) of the sampling clock BCK₂ is 200 μsec (5 kHz in terms offrequency), as depicted in FIG. 11, a movement pitch (the number ofgroups updated among average value data b and c at a front side on atime axis and average value data b and c at a rearmost side throughone-time moving average value calculation) is “2”. As such, if a valueof the movement pitch is optionally set to “m” (m is an integer of 2 ormore), a frequency of the sampling clock signal BCK₂ may be determinedas being 1/m times of the pulse frequency f_(s).

The moving-average-value calculating circuit 114B of the electriccurrent sensor system within the matching device 42 is also operated atthe substantially same time as the moving-average-value calculatingcircuit 106B of the voltage sensor system, and performs the same signalprocess on the average value of the electric current detection signals.

As such, in the present example embodiment, the sampling-average-valuecalculating circuits 104B and 112B perform signal processes on thesampling averages at a high speed during the former and lattermonitoring times T_(L1) and T_(L2) set within the on-period T_(on)(desirably, within time ranges expect the transient time during whichthe power of the reflection wave is high) and the off-period T_(off),respectively, in each cycle of the pulse frequency f_(s), and themoving-average-value calculating circuits 106B and 114B perform signalprocesses on the moving averages for multiple cycles. Further, accordingto a load impedance measurement value, which is obtained from the loadimpedance calculating circuit 116B and updated in synchronization with asampling clock of the moving average, the matching controller 94Bcontinuously controls a reactance of the reactance elements X_(L1) andX_(L2). Thus, even if the pulse frequency for the power modulation isset on the order of several tens of kHz or more and a duty ratio D_(s)is set to a certain level, in a matching operation of the matchingdevice 42, malfunction or life-shortening of operating components(particularly, reactance elements X_(L1) and X_(L2)) may not be caused,and it is possible to accurately follow the change in the load (plasma)impedance.

Herein, the matching device 40 of the high frequency power RF1 justneeds to perform a matching operation on the impedance of plasma duringthe on-period T_(on) as described above, and, thus, as shown on theSmith chart of FIG. 12, the matching operation point A can be equal oras close as possible to the matching point (about 50Ω).

Meanwhile, the matching device 42 of the high frequency power RF2performs a matching operation on both of the impedance of plasma duringthe on-period T_(on) and the impedance of plasma during the off-periodT_(off), and, thus, it is operated to establish the semi-matched staterather than the fully matched state. Herein, since a dual samplingaveraging process is performed as described above in the matching device42, between the on-period T_(on) and the off-period T_(off), a matchingdegree is different depending on the monitoring times (sampling periods)T_(L1) and T_(L2), and is closer to a fully matched state during arelatively long on-period as compared with a short on-period. Therefore,if a duty ratio D_(s) is sufficiently high as depicted in FIG. 9, amatching point B during the on-period T_(on) is closer to the matchingpoint than a matching point C during the off-period T_(off) as shown onthe Smith chart in FIG. 12. Further, the power of the RF2 reflectionwave during the monitoring times (sampling periods) T_(L1) and T_(L2) isinversely proportional to the monitoring time, and is higher during theoff-period T_(off) than during the on-period T_(on) as depicted in FIG.9.

In the example embodiments, the term “fully matched state” refers to astate in which a matching operation point aims to reach the matchingpoint (about 50Ω) regardless of the on-period T_(on) or the off-periodT_(off), and is within a certain (first) approximate range. Further, theterm “semi-matched state” refers to a state in which a matchingoperation point moves around the matching point (about 50Ω) based on adifference in the load impedance between the on-period T_(on) and theoff-period T_(off), and is within a certain (second) approximate rangegreater than the first approximate range.

Even if the power modulation is performed on the high frequency powerRF2 for ion attraction by the second power modulation process, the sameoperation as described above is carried out in both of the matchingdevices 40 and 42 just by replacing the high frequency power RF1(matching device 40) with the high frequency power RF2 (matching device42), and, thus, the same effect as described above can be obtained.

Another Example Embodiment or Modification Example

The preferable example embodiment has been explained, but the presentdisclosure is not limited to the above example embodiment and can bemodified in various ways within a technical scope thereof.

By way of example, as depicted in FIG. 13, the impedance sensor 96Awithin the matching device 40 may include the RF voltage detector 100A,the RF electric current detector 108A, a load impedance calculatingcircuit 120A, a sampling-average-value calculating circuit 122A, and amoving-average-value calculating circuit 124A.

Herein, the load impedance calculating circuit 120A is configured tocalculate a measurement value of load impedance on the high frequencytransmission line 43 based on the RF voltage detection signals and theRF electric current detection signals obtained from the RF voltagedetector 100A and the RF electric current detector 108A, respectively.The load impedance calculating circuit 120A may be an analogue circuitand desirably, may be a digital circuit.

The sampling-average-value calculating circuit 122A and themoving-average-value calculating circuit 124A may perform the samesampling average process as the sampling-average-value calculatingcircuits 104A and 112A and the moving-average-value calculating circuits106A and 114A of the above example embodiment just by replacing a signalto be processed with a load impedance measurement value.

In this case, the matching controller 94A (FIG. 5) controls a reactanceof the reactance elements X_(H1) and X_(H2) via the motors 90A and 92Asuch that a load impedance measurement value obtained from themoving-average-value calculating circuit 124A can be equal orapproximate to the matching point corresponding to impedance on the sideof the high frequency power supply 36.

Likewise, as depicted in FIG. 14, the impedance sensor 96B within thematching device 42 may include the RF voltage detector 100B, the RFelectric current detector 108B, a load impedance calculating circuit120B, a sampling-average-value calculating circuit 122B, and amoving-average-value calculating circuit 124B.

Herein, the load impedance calculating circuit 120B is configured tocalculate a measurement value of load impedance on the high frequencytransmission line 45 based on the RF voltage detection signals and theRF electric current detection signals obtained from the RF voltagedetector 100B and the RF electric current detector 108B, respectively.The load impedance calculating circuit 120B may be an analogue circuitand desirably, may be a digital circuit.

The sampling-average-value calculating circuit 122B and themoving-average-value calculating circuit 124B may perform the samesampling average process as the sampling-average-value calculatingcircuits 104B and 112B and the moving-average-value calculating circuits106B and 114B of the above example embodiment just by replacing a signalto be processed with a load impedance measurement value.

In this case, the matching controller 94B (FIG. 7) controls a reactanceof the reactance elements X_(L1) and X_(L2) via the motors 90B and 92Bsuch that a load impedance measurement value obtained from themoving-average-value calculating circuit 124B can be equal orapproximate to the matching point corresponding to impedance on the sideof the high frequency power supply 38.

In the example embodiments, in the first power modulation process, afirst period during which the high frequency power RF1 has a first leveland a second period during which the high frequency power RF1 has asecond level lower than the first level can be alternately repeated at acertain pulse frequency. Likewise, in the second power modulationprocess, a first period during which the high frequency power RF2 has afirst level and a second period during which the high frequency powerRF2 has a second level lower than the first level can be alternatelyrepeated at a certain pulse frequency.

In the above example embodiment (FIG. 1), the high frequency power RF1for plasma generation is applied to the susceptor (lower electrode) 16.However, the high frequency power RF1 for plasma generation can also beapplied to the upper electrode 46.

The example embodiments are not limited to a capacitively coupled plasmaetching apparatus and can be applied to a capacitively coupled plasmaprocessing apparatus configured to perform various plasma processes suchas plasma CVD, plasma ALD, plasma oxidation, plasma nitrification,sputtering, and the like. Further, the processing target substrate ofthe example embodiments may not be limited to the semiconductor wafer,but various types of substrates for a flat panel display, an organic ELor a solar cell, or a photo mask, a CD substrate, and a printed circuitboard may also be used.

EXPLANATION OF REFERENCE NUMERALS

-   -   10: Chamber    -   16: Susceptor (Lower electrode)    -   36: High frequency power supply (for plasma generation)    -   38: High frequency power supply (for ion attraction)    -   40, 42: Matching devices    -   43, 45: High frequency transmission lines    -   46: Upper electrode (Shower head)    -   56: Processing gas supply source    -   72: Main control unit    -   88A, 88B: Matching circuits    -   94A, 94B: Matching controllers    -   96A, 96B: Impedance sensors    -   100A, 100B: RF voltage detectors    -   102A, 102B: Voltage-detection-signal generating circuits    -   104A, 104B: Sampling-average-value calculating circuits    -   112A, 112B: Sampling-average-value calculating circuits    -   106A, 106B: Moving-average-value calculating circuits    -   114A, 114B: Moving-average-value calculating circuits    -   116A, 116B: Load impedance calculating circuits    -   120A, 120B: Load impedance calculating circuits    -   122A, 122B: Sampling-average-value calculating circuits    -   124A, 124B: Moving-average-value calculating circuits

We claim:
 1. A plasma processing apparatus of generating plasma by highfrequency discharge of a processing gas between a first electrode and asecond electrode which are provided to face each other within anevacuable processing vessel that accommodates therein a substrate to beprocessed, which is loaded into and unloaded from the processing vessel,and performing a process on the substrate held on the first electrodeunder the plasma, the plasma processing apparatus comprising: a firsthigh frequency power supply configured to output a first high frequencypower having a frequency suitable for ion attraction into the substrateon the first electrode from the plasma; a first high frequencytransmission line configured to transmit the first high frequency poweroutputted from the first high frequency power supply to the firstelectrode; a first matching device configured to match impedance on theside of the first high frequency power supply with load impedance on thefirst high frequency transmission line; a second high frequency powersupply configured to output a second high frequency power having afrequency suitable for plasma generation; a second high frequencytransmission line configured to transmit the second high frequency poweroutputted from the second high frequency power supply to any one of thefirst electrode and the second electrode; a second matching deviceconfigured to match impedance on the side of the second high frequencypower supply with load impedance on the second high frequencytransmission line; and a high frequency power modulation unit configuredto control the second high frequency power supply such that a firstperiod during which the second high frequency power is on or has a firstlevel and a second period during which the second high frequency poweris off or has a second level lower than the first level is alternatelyrepeated at a predetermined pulse frequency, wherein the first matchingdevice includes: a matching circuit having a variable reactance elementprovided on the first high frequency transmission line; asampling-average-value calculating circuit configured to sample voltagedetection signals and electric current detection signals correspondingto the first high frequency power on the first high frequency supplyline with a preset sampling frequency and calculate an average value ofthese signals during a first monitoring time set for both of the firstperiod and the second period in each cycle of the pulse frequency; amoving-average-value calculating circuit configured to calculate amoving average value of the voltage detection signals and the electriccurrent detection signals based on an average value obtained from thesampling-average-value calculating circuit in each cycle; a loadimpedance-measurement-value calculating circuit configured to calculatea measurement value of the load impedance with respect to the first highfrequency power supply based on the moving average value of the voltagedetection signals and the electric current detection signals obtainedfrom the moving-average-value calculating circuit; and a matchingcontroller configured to vary a reactance of the variable reactanceelement such that the measurement value of the load impedance obtainedfrom the load impedance-measurement-value calculating circuit is equalor approximate to a preset matching point corresponding to impedance onthe side of the first high frequency power supply.
 2. A plasmaprocessing apparatus of generating plasma by high frequency discharge ofa processing gas between a first electrode and a second electrode whichare provided to face each other within an evacuable processing vesselthat accommodates therein a substrate to be processed, which is loadedinto and unloaded from the processing vessel, and performing a processon the substrate held on the first electrode under the plasma, theplasma processing apparatus comprising: a first high frequency powersupply configured to output a first high frequency power having afrequency suitable for ion attraction into the substrate on the firstelectrode from the plasma; a first high frequency transmission lineconfigured to transmit the first high frequency power outputted from thefirst high frequency power supply to the first electrode; a firstmatching device configured to match impedance on the side of the firsthigh frequency power supply with load impedance on the first highfrequency transmission line; a second high frequency power supplyconfigured to output a second high frequency power having a frequencysuitable for plasma generation; a second high frequency transmissionline configured to transmit the second high frequency power outputtedfrom the second high frequency power supply to any one of the firstelectrode and the second electrode; a second matching device configuredto match impedance on the side of the second high frequency power supplywith load impedance on the second high frequency transmission line; anda high frequency power modulation unit configured to control the secondhigh frequency power supply such that a first period during which thesecond high frequency power is on or has a first level and a secondperiod during which the second high frequency power is off or has asecond level lower than the first level is alternately repeated at apredetermined pulse frequency, wherein the first matching deviceincludes: a matching circuit having a variable reactance elementprovided on the first high frequency transmission line; asampling-average-value calculating circuit configured to samplemeasurement values of the load impedance on the first high frequencytransmission line with a preset sampling frequency and calculate anaverage value of the measurement values during a first monitoring timeset for both of the first period and the second period in each cycle ofthe pulse frequency; a moving-average-value calculating circuitconfigured to calculate a moving average value of the measurement valuesof the load impedance based on the average value obtained from thesampling-average-value calculation circuit in each cycle; and a matchingcontroller configured to vary a reactance of the variable reactanceelement such that the moving average value of the measurement values ofthe load impedance obtained from the moving-average-value calculatingcircuit is equal or approximate to a preset matching point correspondingto the impedance on the side of the first high frequency power supply.3. A plasma processing apparatus of generating plasma by high frequencydischarge of a processing gas between a first electrode and a secondelectrode which are provided to face each other within an evacuableprocessing vessel that accommodates therein a substrate to be processed,which is loaded into and unloaded from the processing vessel, andperforming a process on the substrate held on the first electrode underthe plasma, the plasma processing apparatus comprising: a first highfrequency power supply configured to output a first high frequency powerhaving a frequency suitable for plasma generation; a first highfrequency transmission line configured to transmit the first highfrequency power outputted from the first high frequency power supply toany one of the first electrode and the second electrode; a firstmatching device configured to match impedance on the side of the firsthigh frequency power supply with load impedance on the first highfrequency transmission line; a second high frequency power supplyconfigured to output a second high frequency power having a frequencysuitable for ion attraction into the substrate on the first electrodefrom the plasma; a second high frequency transmission line configured totransmit the second high frequency power outputted from the second highfrequency power supply to the first electrode; a second matching deviceconfigured to match impedance on the side of the second high frequencypower supply with load impedance on the second high frequencytransmission line; and a high frequency power modulation unit configuredto control the second high frequency power supply such that a firstperiod during which the second high frequency power is on or has a firstlevel and a second period during which the second high frequency poweris off or has a second level lower than the first level is alternatelyrepeated at a predetermined pulse frequency, wherein the first matchingdevice includes: a matching circuit having a variable reactance elementprovided on the first high frequency transmission line; asampling-average-value calculating circuit configured to sample voltagedetection signals and electric current detection signals correspondingto the first high frequency power on the first high frequency supplyline with a preset sampling frequency and calculate an average value ofthese signals during a first monitoring time set for both of the firstperiod and the second period in each cycle of the pulse frequency; amoving-average-value calculating circuit configured to calculate amoving average value of the voltage detection signals and the electriccurrent detection signals based on an average value obtained from thesampling-average-value calculating circuit in each cycle; a loadimpedance-measurement-value calculating circuit configured to calculatea measurement value of the load impedance with respect to the first highfrequency power supply based on the moving average value of the voltagedetection signals and the electric current detection signals obtainedfrom the moving-average-value calculating circuit; and a matchingcontroller configured to vary a reactance of the variable reactanceelement such that the measurement value of the load impedance obtainedfrom the load impedance-measurement-value calculating circuit is equalor approximate to a preset matching point corresponding to impedance onthe side of the first high frequency power supply.
 4. A plasmaprocessing apparatus of generating plasma by high frequency discharge ofa processing gas between a first electrode and a second electrode whichare provided to face each other within an evacuable processing vesselthat accommodates therein a substrate to be processed, which is loadedinto and unloaded from the processing vessel, and performing a processon the substrate held on the first electrode under the plasma, theplasma processing apparatus comprising: a first high frequency powersupply configured to output a first high frequency power having afrequency suitable for plasma generation; a first high frequencytransmission line configured to transmit the first high frequency poweroutputted from the first high frequency power supply to any one of thefirst electrode and the second electrode; a first matching deviceconfigured to match impedance on the side of the first high frequencypower supply with load impedance on the first high frequencytransmission line; a second high frequency power supply configured tooutput a second high frequency power having a frequency suitable for ionattraction into the substrate on the first electrode from the plasma; asecond high frequency transmission line configured to transmit thesecond high frequency power outputted from the second high frequencypower supply to the first electrode; a second matching device configuredto match impedance on the side of the second high frequency power supplywith load impedance on the second high frequency transmission line; anda high frequency power modulation unit configured to control the secondhigh frequency power supply such that a first period during which thesecond high frequency power is on or has a first level and a secondperiod during which the second high frequency power is off or has asecond level lower than the first level is alternately repeated at apredetermined pulse frequency, wherein the first matching deviceincludes: a matching circuit having a variable reactance elementprovided on the first high frequency transmission line; asampling-average-value calculating circuit configured to samplemeasurement values of the load impedance on the first high frequencytransmission line with a preset sampling frequency and calculate anaverage value of the measurement values during a first monitoring timeset for both of the first period and the second period in each cycle ofthe pulse frequency; a moving-average-value calculating circuitconfigured to calculate a moving average value of the measurement valuesof the load impedance based on the average value from thesampling-average-value calculating circuit in each cycle; and a matchingcontroller configured to vary a reactance of the variable reactanceelement such that the moving average value of the measurement values ofthe load impedance obtained from the moving-average-value calculatingcircuit is equal or approximate to a preset matching point correspondingto the impedance on the side of the first high frequency power supply.5. The plasma processing apparatus of claim 1, wherein the firstmonitoring time does not include a first transient time right afterstarting the first period during the first period.
 6. The plasmaprocessing apparatus of claim 1, wherein the first monitoring time doesnot include a second transient time right before ending the first periodduring the first period.
 7. A plasma processing apparatus of generatingplasma by high frequency discharge of a processing gas between a firstelectrode and a second electrode which are provided to face each otherwithin an evacuable processing vessel that accommodates therein asubstrate to be processed, which is loaded into and unloaded from theprocessing vessel, and performing a process on the substrate held on thefirst electrode under the plasma, the plasma processing apparatuscomprising: a high frequency power supply configured to output a highfrequency power for plasma generation; a high frequency transmissionline configured to transmit the high frequency power outputted from thehigh frequency power supply to any one of the first electrode and thesecond electrode; a matching device configured to match impedance on theside of the high frequency power supply with load impedance on the highfrequency transmission line; and a high frequency power modulation unitconfigured to control the high frequency power supply such that a firstperiod during which the high frequency power is on and a second periodduring which the high frequency power is off is alternately repeated ata predetermined pulse frequency, wherein the matching device includes: amatching circuit having a variable reactance element provided on thehigh frequency transmission line; a sampling-average-value calculatingcircuit configured to sample voltage detection signals and electriccurrent detection signals corresponding to the high frequency power onthe high frequency supply line with a preset sampling frequency andcalculate an average value of these signals during a monitoring time setfor the first period in each cycle of the pulse frequency; amoving-average-value calculating circuit configured to calculate amoving average value of the voltage detection signals and the electriccurrent detection signals based on the average value obtained from thesampling-average-value calculating circuit in each cycle; a loadimpedance-measurement-value calculating circuit configured to calculatea measurement value of the load impedance with respect to the highfrequency power supply based on the moving average value of the voltagedetection signals and the electric current detection signals obtainedfrom the moving-average-value calculating circuit; and a matchingcontroller configured to vary a reactance of the variable reactanceelement such that the measurement value of the load impedance obtainedfrom the load impedance-measurement-value calculating circuit is equalor approximate to a preset matching point corresponding to the impedanceon the side of the high frequency power supply.
 8. A plasma processingapparatus of generating plasma by high frequency discharge of aprocessing gas between a first electrode and a second electrode whichare provided to face each other within an evacuable processing vesselthat accommodates therein a substrate to be processed, which is loadedinto and unloaded from the processing vessel, and performing a processon the substrate held on the first electrode under the plasma, theplasma processing apparatus comprising: a high frequency power supplyconfigured to output a high frequency power for plasma generation; ahigh frequency transmission line configured to transmit the highfrequency power outputted from the high frequency power supply to anyone of the first electrode and the second electrode; a matching deviceconfigured to match impedance on the side of the high frequency powersupply with load impedance on the high frequency transmission line; anda high frequency power modulation unit configured to control the highfrequency power supply such that a first period during which the highfrequency power is on and a second period during which the highfrequency power is off is alternately repeated at a predetermined pulsefrequency, wherein the matching device includes: a matching circuithaving a variable reactance element provided on the high frequencytransmission line; a sampling-average-value calculating circuitconfigured to sample measurement values of the load impedance on thehigh frequency transmission line with a preset sampling frequency andcalculate an average value of the measurement values during a monitoringtime set for the first period in each cycle of the pulse frequency; amoving-average-value calculating circuit configured to calculate amoving average value of the measurement values of the load impedancebased on the average value obtained from the sampling-average-valuecalculating circuit in each cycle; and a matching controller configuredto vary a reactance of the variable reactance element such that themoving average value of the measurement values of the load impedanceobtained from the moving-average-value calculating circuit is equal orapproximate to a preset matching point corresponding to the impedance onthe side of the high frequency power supply.
 9. The plasma processingapparatus of claim 7, wherein the monitoring time does not include afirst transient time right after starting the first period during thefirst period.
 10. The plasma processing apparatus of claim 7, whereinthe monitoring time does not include a second transient time rightbefore ending the first period during the first period.
 11. The plasmaprocessing apparatus of claim 7, wherein the monitoring time is not setwithin the second period.
 12. The plasma processing apparatus of claim1, wherein the high frequency power modulation unit is configured tovary at least one of the pulse frequency or a ratio, which is a dutyratio, of the first period in each cycle of the pulse frequency withrespect to an entire time in each cycle thereof.